(1) Field of the Invention
The present invention relates to an optical transmission module used in a high-speed optical fiber communication, and specifically relates to a low-cost optical transmission module.
(2) Description of the Related Art
A general optical transmission module includes a light-emitting device, a light-receiving device, and a driving device that are arranged on a substrate. The light-receiving device monitors light emitted backward from the light-emitting device. The driving device drives the light-emitting device. On the substrate, wiring patterns for electrically connecting the devices are formed.
Meanwhile, a high-frequency electric current is applied to drive the light-emitting device at high speeds, and the high-frequency electric current flows through the wiring pattern connecting the driving device and the light-emitting device. For this reason, when an optical transmission module is designed, it is necessary to take into consideration the parasitic inductance and the parasitic capacitance that affect the high-frequency electric current.
Japanese Laid-Open Patent Application No. 2002-151782 discloses a light-emitting apparatus that includes a light-emitting device, a driving device, and a light-receiving device that are arranged in the stated order on a substrate. In the conventional light-emitting apparatus with this construction, the backward light emitted from the light-emitting device is guided so as to bypass the driving device and pass through an optical guide groove, which is formed in the substrate, to reach the light-receiving device. With such a construction, it is possible to arrange the light-emitting device and the driving device close to each other. This enables the wiring pattern connecting these devices to be reduced in length. This means that the parasitic inductance and the parasitic capacitance generated in this wiring pattern are reduced.
FIG. 14 is a plane view of the light-emitting apparatus disclosed in Japanese Laid-Open Patent Application No. 2002-151782. FIG. 15 is a cross section of the light-emitting apparatus.
A light-emitting apparatus 2000 includes LD (Laser Diode) 2002, IC (Integrated Circuit) 2003, and PD (PhotoDiode) 2004 that are arranged in the stated order on a substrate 2010, where the LD 2002 is a light-emitting device, the IC 2003 is a driving device, and the PD 2004 is a monitoring light-receiving device.
An optical guide groove 2005 is formed on the substrate 2010 so that light 2006 emitted from the LD 2002 bypasses the IC 2003 and reaches a light-receiving unit 2007 of the PD 2004.
However, to manufacture the light-emitting apparatus 2000, it is required to adjust the positions of the LD 2002 and the PD 2004 accurately, so that the light 2006 emitted from the LD 2002 is received by the light-receiving unit 2007 of the PD 2004 via the optical guide groove 2005. Also, it is required to form the optical guide groove 2005 accurately. These are problematic factors in terms of the mass productivity or the production cost.